JPH07130372A - Solid polymer fuel cell electrode and method for producing the same - Google Patents

Abstract

(57) [Summary] [Structure] An electrode for a polymer electrolyte fuel cell of a type using a mixture of catalyst particles, a polymer electrolyte and PTFE,
The entire surface layer of this electrode is coated with a polymer electrolyte. [Effect] In a solid polymer fuel cell electrode of a type using a mixture of catalyst particles, a polymer electrolyte and PTFE,
By coating the entire surface layer of the electrode with a polymer electrolyte, the characteristics of the electrode can be improved, and the performance of a battery using the same can be significantly improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an electrode for a polymer electrolyte fuel cell, more specifically, a method for producing an electrode for a polymer electrolyte fuel cell, in which gas diffusion on the electrode layer surface is carried out. Concerning the treatment method of layers.

[0002]

2. Description of the Related Art A polymer electrolyte fuel cell is characterized in that an ionic conductor, that is, an electrolyte, is a solid and a polymer. A resin film or the like is used, and both electrodes of the negative electrode and the positive electrode are arranged with the polymer electrolyte sandwiched therebetween. For example, hydrogen is supplied to the negative electrode side and oxygen or air is supplied to the positive electrode side to cause an electrochemical reaction. , To generate electricity.

As both the negative electrode and the positive electrode in contact with the solid polymer electrolyte, a type in which catalyst particles for promoting the reaction are added to the electrode has been developed. Various methods have been proposed so far for the method of manufacturing an electrode in which a catalyst is added and used, and as one system, the catalyst particles are further mixed with polyperfluoroethylene (PTFE). The form is known.

For example, in US Pat. No. 3,297,484, catalyst particles such as platinum black and palladium black, or a kneaded product obtained by mixing catalyst particles in which these are supported on carbon particles with polytetrafluoroethylene (PTFE) is used as an electrode system. And a method of thermocompression-bonding this to an ion exchange resin membrane as a polymer electrolyte is also disclosed in US Pat.
In the specification of No. 32355, the kneaded product is separately treated with PTFE.
A method has been proposed in which the film is applied as a slurry to form an electrode sheet, and the electrode sheet is thermocompression bonded to an ion exchange resin membrane as a polymer electrolyte.

In this technique, such mixing of PTFE with the catalyst particles is mainly for binding and binding the catalyst components forming the catalyst layer in the electrode sheet. If the polymer electrolyte and the electrode sheet are simply bonded to each other, the reaction site (reaction region) is limited to the two-dimensional interface between the two, and the substantial working area is small.

Therefore, as one of the techniques for improving this, a carbon powder carrying a catalyst metal, a styrene-divinyl sulfonic acid resin powder, and a polystyrene are added to a styrene-divinyl benzene sulfonic acid resin membrane as a solid electrolyte. It has been proposed that the electron-ion mixed conductor layer made of a mixture with a binder is bonded to increase the number of contacts between the electrode material and the solid polymer electrolyte, thereby achieving three-dimensional reaction sites.

Electrochemistry, 53, No. 10 (198
5), pp. 812-817, introduces the above three-dimensionalization technology, and in such a polymer electrolyte fuel cell using a styrene-divinylbenzene-based ion exchange resin membrane as an electrolyte, electron-ion mixed conduction is used. Even with the body layer,
After pointing out that there are problems such as low current density that can be taken out, an attempt to increase the working area by introducing three-dimensional reaction sites was introduced in the case of using an alternative perfluorocarbon sulfonic acid resin film. ing.

According to this, NA, which is a kind of perfluorocarbon sulfonic acid resin membrane, is used as the solid polymer electrolyte.
A FION film is used, and a platinum electrode is bonded to one surface of the NAFION film by an electroless plating method (permeation method) to form a hydrogen electrode, that is, an anode side electrode. The negative electrode is manufactured by the following steps.

First, as the electrode catalyst powder for the oxygen electrode, platinum black powder or carbon powder carrying 10% platinum (hereinafter referred to as "platinum-supporting carbon powder") is used.
Amberlite IR-120B (T-3) [styrene-divinylbenzenesulfonic acid resin, Na type, powder having a particle size of 30 μm, manufactured by Organo, trade name) or NA
FION-117 (perfluorocarbon sulfonic acid resin, H type, 5% solution in a mixed solvent of aliphatic alcohol and water, manufactured by Aldrich Chemical Company, trade name)
Are mixed in various mixing ratios.

Then, for each of the above mixtures, PTFE was added.
Is added in the form of an aqueous suspension in the case of platinum black powder in a solid content weight ratio of 30%, and in the case of platinum-supporting carbon powder 60% in the same manner, and the mixture is kneaded. After being vacuum dried, the oxygen electrode sheet is heated at a temperature of 100 ° with respect to the NAFION membrane as a solid polymer electrolyte.
C, hot pressing is performed at a pressure of 210 kg / cm ² .

According to this, by mixing the ion exchange resin into the oxygen electrode integrally bonded to the NAFION membrane as the solid polymer electrolyte, the electrode reaction site is made three-dimensional, and thereby, It is pointed out that the polarization characteristics can be remarkably improved, and that the effect of mixing the ion exchange resin is particularly large when the platinum-supported carbon is used as the electrode catalyst.

In this case, catalyst particles composed of platinum black powder or platinum-supported carbon powder are coated with a polymer electrolyte mixed therein, and in the case of the above "platinum black powder, solid weight ratio. At 30%,
In the case of platinum-supporting carbon powder, PTFE added in the same proportion of 60% corresponds to the binder.

In the above techniques, the electrode sheet is produced by sheeting the kneaded material of the electrode material by rolling or the like except the case of US Pat. No. 3,432,355. As a mode of producing this electrode sheet, that is, forming a sheet, a porous paper or sheet is separately used as a base material, and a catalyst layer forming component such as catalyst particles is supported on the porous paper or sheet. There is also a formal method.

In this case, as the paper or sheet, for example, a carbon paper having a predetermined porosity and thickness is used, while a PTFE-based disperser is used.
After impregnation with John, heat treatment is carried out to deposit and carry electrode constituent components such as catalyst particles on the water repellent carbon paper. One example thereof is Japanese Patent Publication No. 4-16.
There is 2365 publication.

The technique of this publication is characterized in that a mixture of carbon black supporting a platinum catalyst and carbon black not supporting a catalyst is used as the fine powder for the catalyst layer constituting the electrode sheet. However, a water-repellent carbon paper is used for the sheet formation, and a mixture of fine powder containing catalyst particles is sprayed on the water-repellent carbon paper. They are attached by pressing under heat and again, these catalyst particles are coated with an ion exchange resin and treated with PTFE.

The present inventor has instead developed a method for simplifying the manufacturing process without using PTFE and manufacturing an electrode for a polymer electrolyte fuel cell excellent in cell performance, and applied for a patent in advance. (Japanese Patent Application No. 4-35805
No. 8, Japanese Patent Application No. 4-358059), and even in this case, there is no difference in using such a water repellent carbon paper as the base sheet.

In the above technique, platinum-supported carbon black as catalyst particles and a solid polymer electrolyte (ion exchange resin) are used as a slurry in a solvent, and the slurry is formed on a water-repellent carbon paper. It is applied in the form of a powder or is deposited and adhered by a filtration method. According to the research results thereafter, it is possible to add and use PTFE in the slurry, and further effective effect can be obtained. ing.

As described above, regardless of whether or not the water repellent carbon paper is used, the solid polymer fuel cell in which the catalyst particles and the polymer electrolyte mixed with the catalyst particles are incorporated is used. Among them, the catalyst particles coexist with the polymer electrolyte and the gas phase, and it is possible to improve the performance of the battery by securing more three-phase interfaces, but when PTFE is added to this, However, not only as a binder, but also as an effect of securing a gas phase, it also has a non-conductive surface.

[0019]

The present inventor continues to research and study the manufacturing process of the electrode, including the function and action of the gas diffusion layer, and the whole surface of the catalyst layer. It has been found that the characteristics of this electrode can be improved by coating the solid polymer electrolyte with a solid polymer electrolyte, and the performance of a fuel cell incorporating the same can be markedly improved, and the present invention has been reached. .

That is, the present invention is a method for producing an electrode for a polymer electrolyte fuel cell of the type using a mixture of catalyst particles, a polymer electrolyte and polytetrafluoroethylene (PTFE), and the entire surface layer of this electrode is It is intended to improve the characteristics of the electrode obtained through this step by adding the step of coating with a solid polymer electrolyte and to markedly improve the performance of a battery incorporating this.

[0021]

The present invention relates to a solid polymer electrolyte fuel cell electrode of the type using a mixture of catalyst particles, a polymer electrolyte and PTFE, and the entire surface layer of the electrode is made of a solid polymer electrolyte. The present invention provides an electrode for a polymer electrolyte fuel cell, which is characterized by being coated.

Further, the present invention is a method for producing an electrode for a polymer electrolyte fuel cell of the type using a mixture of catalyst particles, a polymer electrolyte and polytetrafluoroethylene, wherein the entire surface layer of the electrode is a solid polymer. Provided is a method for producing an electrode for a polymer electrolyte fuel cell, which is characterized by adding a step of coating with an electrolyte.

In this case, styrene-divinylbenzene sulfonic acid resin, perfluorocarbon sulfonic acid resin, etc. can be used as the solid polymer electrolyte for coating. do it,
For example, it is advantageous to use a perfluorocarbon sulfonic acid resin such as NAFION.

As the catalyst particles, conventionally known catalysts such as platinum black powder, platinum alloy powder, platinum-supporting carbon black, and palladium black powder can be used as they are in the known form. From the viewpoint of making the electrode reaction site three-dimensional or securing more three-phase interfaces, these particles are coated with, for example, a perfluorocarbon sulfonic acid resin-based solid polymer electrolyte. It is desirable to have.

Further, the solid polymer fuel cell electrode is
It is usually applied as an electrode sheet, and the sheet is
As the catalyst formation, the catalyst constituent material is adhered to the solid polymer electrolyte membrane as the battery body, the catalyst constituent material is kneaded into a sheet by rolling, etc. It is carried out in various modes such as being attached to a water repellent carbon paper as a sheet, but the present invention is applicable to the sheet obtained in any of these modes.

In the present invention, among these, a suspension of the catalyst constituent material consisting of catalyst particles, an electrolyte and PTFE is attached to a water repellent carbon paper as a base sheet. It is particularly advantageous in the case of adopting the mode that the above-mentioned is adopted, and in addition to the excellent advantages that this mode itself has, the effect of the present invention can be obtained more effectively. In this case, the water repellent agent for the paper is preferably a PTFE (tetrafluoroethylene) type. Where PTFE
The term “(tetrafluoroethylene) type” is meant to include a tetrafluoroethylene-hexafluoropropylene copolymer and other copolymers thereof.

[0027]

EXAMPLES Examples of the present invention will be described below, but it goes without saying that the present invention is not limited to these examples. First, catalyst particles were prepared by supporting platinum black at a ratio of 50% by weight with respect to carbon black particles, and the amount of NAFIO was 20% by weight based on the total amount of the particles.
N-117 (perfluorocarbon sulfonic acid resin, D
u Pont, trade name) alcohol solution,
Mix evenly.

Next, the solvent was removed from this mixed solution, but this operation was carried out by heating from below the mixed solution container in a vacuum at a temperature of 50 ° C. for 12 hours. -Tited catalyst particles were obtained, to which distilled water was added to make an aqueous suspension.

On the other hand, the porosity is 80% and the thickness is 0.4 mm.
The carbon paper was impregnated with a dispersion of NEOFLON (registered trademark, manufactured by Daikin Industries, Ltd., tetrafluoroethylene-hexafluoropropylene copolymer) and then heat-treated to make the water-repellent NEOFLON. -A bomber was obtained. In this case, the quantitative ratio was adjusted so that neofuron accounted for 20% by weight in the total amount.

Next, the suspension of the catalyst particles obtained above was filtered on the water repellent carbon paper obtained above.
Each coating catalyst particle was uniformly deposited on the water repellent carbon paper. In the case of this filtration operation, in the case of this example, a water-repellent carbon paper is placed on a perforated plate and the above suspension is poured on it while depressurizing the lower part to allow only the solvent to permeate. , The so-called Nutze funnel format.

In this case, the filtration operation should be carried out not by such a Nutze funnel type but by a mode in which the suspension is poured onto a dewatering carbon paper while being pressurized from above. It is also possible to use both methods together. The layer deposited on the above water repellent carbon paper is the catalyst layer, and the composition of the present invention, that is, NA as a kind of solid polymer electrolyte, is continuously applied to the spray surface.
After spraying the alcohol solution of FION-117 and impregnating it with the catalyst layer, the temperature was raised to 80 ° C and the temperature was changed to 12%.
It was heated for hours and the solvent was evaporated off.

As a comparative example (conventional example),
Of the above steps, step (3) is not carried out, that is, an alcohol solution of NAFION-117 (solid polymer electrolyte) is applied to the surface of the catalyst layer deposited on the water repellent carbon paper. An electrode sheet was prepared in the same manner except that the step of spraying and impregnating the catalyst layer with the catalyst layer was not performed, and the electrode sheet was used as a comparative example (conventional example).

In the following, the electrode sheet prepared in the above steps to as a comparative example is used, and after being integrated with a solid polymer electrolyte membrane, it is set for a solid polymer fuel cell, and a battery is prepared. An example of measuring and observing a change in performance as described above will be described.

The electrode sheet produced by the above steps
Was used in combination with a solid polymer electrolyte membrane, and both were set. This is a solid polymer electrolyte membrane (NAFION-117 membrane) between the two electrode sheets prepared above.
It was made by pressing for 60 seconds under a pressure of 100 kgf / cm ² at a temperature of 140 ° C., and this was used as a test battery.

Further, the electrode sheet produced for the comparative example above, that is, the electrode sheet produced without carrying out the steps of the above-mentioned steps is used, and the sheet between the two sheets is used. Solid polymer electrolyte membrane (NAFION-11
7 film), temperature 140 ° C, pressure 100 kgf / c
It was produced by pressing under a pressure of m ² for 60 seconds, and this was used as a test battery for a comparative example.

In this embodiment, hydrogen is used as the fuel,
While this was supplied to the anode side, oxygen was supplied to the cathode side. The supply pressures of both gases were both 2 atm, hydrogen was humidified at 75 ° C., oxygen was humidified at 25 ° C., and the temperature of the battery was maintained at 60 ° C. for measurement.

FIG. 1 shows the relationship between the cell density and the current density measured for each test battery as described above. According to this, in the example, the voltage is
From the initial stage, it is as high as 0.8 to 0.9 V, and it can be seen that even if the current density is increased, almost the same tendency is exhibited. As described above, in the present invention, the characteristics of the electrode can be improved, and the performance of the battery using the same can be significantly improved.

[0038]

As described above, according to the present invention, in a solid polymer fuel cell electrode of a type using a mixture of catalyst particles, a polymer electrolyte and PTFE, the entire surface layer of the electrode is a solid polymer. By coating with an electrolyte, the characteristics of the electrode can be improved, and the performance of a battery using the same can be significantly improved.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the measured current density and cell voltage of each of the test batteries manufactured in Examples and Comparative Examples.

Claims (6)

[Claims] 1. A solid polymer fuel cell electrode of the type using a mixture of catalyst particles, a polymer electrolyte and polytetrafluoroethylene, wherein the entire surface layer of the electrode is coated with the polymer electrolyte. An electrode for a polymer electrolyte fuel cell, which is characterized in that: 2. The solid polymer type of claim 1, wherein the surface layer of the electrode is a surface layer formed on a water repellent carbon paper as a base sheet. Electrodes for fuel cells. 3. The polymer fuel cell electrode according to claim 1, wherein the polymer electrolyte is a perfluorocarbon sulfonic acid resin. 4. A method for producing an electrode for a polymer electrolyte fuel cell of the type using a mixture of catalyst particles, a polymer electrolyte and polytetrafluoroethylene, wherein the entire surface layer of the electrode is coated with the polymer electrolyte. A method for producing an electrode for a polymer electrolyte fuel cell, comprising: 5. The solid polymer type as claimed in claim 4, wherein the surface layer of the electrode is a surface layer formed on a water repellent carbon paper as a base sheet. Manufacturing method of fuel cell electrode. 6. The method for producing an electrode for a polymer electrolyte fuel cell according to claim 4, wherein the polymer electrolyte is a perfluorocarbon sulfonic acid resin.